This invention relates to variable data printing. More specifically, it relates to variable data lithographic printing device and process.
Lithographic printing surface generally consists of ink-receptive areas (image areas) and ink-repelling areas (non-image areas). During printing operation, an ink is preferentially received in the image areas, not in the non-image areas, and then transferred to the surface of a material upon which the image is to be produced.
Lithographic printing can be further divided into two general types: wet lithographic printing and waterless lithographic printing. In wet lithographic printing members, the ink-receptive areas consist of oleophilic materials and the ink-repelling areas consist of hydrophilic materials; fountain solution (consisting of primarily water) is required to continuously dampen the hydrophilic materials during printing operation to make the non-image areas oleophobic. In waterless lithographic printing members, the ink-receptive areas consist of oleophilic materials and the ink-repelling areas consist of oleophobic materials; no dampening with fountain solution is required.
At the present time, lithographic printing is generally performed on a lithographic printing press. The lithographic printing member can be a typical lithographic printing plate mounted on the plate cylinder. The plate can be imaged and processed before or after mounted on press. Examples of such a printing process are described in U.S. Pat. Nos. 5,700,619, 5,466,557, 5,491,045 and 5,955,238 (for off-press imaging and process), and U.S. Pat. Nos. 5,258,263, 5,395,734, 5,516,620, 6,030,750, 6,014,929, 6,071,675, and 6,242,156 (for on-press development).
Alternatively, the lithographic printing member can be formed on press by coating a photosensitive layer onto a plate cylinder surface or onto a plate substrate mounted on a plate cylinder. The on-press formed printing member can be imagewise exposed and processed on press before lithographic printing. After the completion of a printing operation, the hardened imaging layer on the plate cylinder can be cleaned off to allow reuse of the cylinder or substrate surface for preparing another printing member. Such a printing system is commonly called plateless press. Examples of such a plateless press are described in U.S. Pat. Nos. 5,713,287 and 6,298,780.
While lithographic printing process as described above has played a major role in printing and publishing industrial for decades, the application of lithographic printing so far is limited to making multiple copies (usually a few hundreds to a few millions copies).
In variable data printing application wherein each copy printed has different imaging, inkjet printing and electrophotographic (or called Xerox) laser printing are the most widely used methods, as evidenced by widely used desktop inkjet printer and laser printer. Other printing methods, such as thermal paper and thermal dye transfer, also play an important role, as evidenced by some facsimile printers. While these current variable data printing methods are very useful, the printing quality by these methods is inferior to that by lithographic printing in resolution, color density and imaging stability. For example, material printed with inkjet printer has limited resolution and imaging stability; material printed with thermal printer has limited color density and imaging stability; and material printed with Xerox laser printer has limited resolution and toner-to-medium adhesion.
It would be desirable if a variable data printing device can be designed based on lithographic printing principle. This would allow improved resolution, color density, and imaging stability.
It is an object of this invention to provide a lithographic printing device suitable for variable data printing.
It is another object of this invention to provide a lithographic printing device and process which allow continuous photosensitive layer coating, imagewise exposure, development, formation of inked imaging, transfer of the inked imaging to a receiving surface, and recovering of the substrate surface during printing process.
It is another object of this invention to provide a lithographic printing device and process which allow continuous formation or supply of pre-sensitized lithographic printing surface, imagewise exposure, development, formation of inked imaging, transfer of the inked imaging to a receiving surface during printing process.
Further objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments.
According to the present invention, there has been provided a variable data lithographic printing device comprising:
(a) a printing cylinder;
(b) a coating means for depositing a photosensitive layer on the cylinder surface, wherein said photosensitive layer is soluble or dispersible in ink and/or fountain solution, capable of hardening upon exposure to an actinic radiation, and exhibits an affinity or aversion substantially opposite to the affinity or aversion of said cylinder surface to at least one printing liquid selected from the group consisting of ink and an abhesive fluid for ink;
(c) an exposure means for providing the actinic radiation to the cylinder surface according to digital imaging information;
(d) an inking means for applying ink or both fountain solution and ink to the cylinder surface; and
(e) an erasing means for removing the remaining photosensitive layer and leftover ink to recover the cylinder surface;
(f) wherein the means (b) to (e) are mounted proximate the cylinder surface and sequentially arranged along the cylinder surface in the rotating direction of the cylinder; and each means of (b) to (e) completes its designed function (coating, imaging, inking, or erasing) to the cylinder surface areas in the designed printing width which pass by said means in each single pass during printing operation.
According to another aspect of the present invention, there has been provided a method of variable data lithographic printing, comprising:
(a) providing a lithographic printing device as described above;
(b) continuously depositing the photosensitive layer on the cylinder surface;
(c) continuously exposing the plate with an actinic radiation to cause hardening of the photosensitive layer in the exposed areas according to digital imaging information;
(d) continuously applying ink or both fountain solution and ink to the cylinder surface to remove the non-hardened areas of the photosensitive layer and to form inked imaging on the cylinder surface;
(e) continuously lithographically printing images from said cylinder surface to a receiving surface; and
(f) continuously removing the hardened photosensitive layer and leftover ink to bare the cylinder surface.
The above printing systems can be designed in a way so that the hardened photosensitive layer is capable of transferring with ink to the receiving surface, or the hardened photosensitive layer and leftover ink are capable of dissolving or dispersing into the photosensitive layer coating fluid from the coating means. In either system, the erasing means can be omitted.
For the above variable data lithographic printing device of this invention, the printing cylinder can be replaced with a substrate ribbon supply means for passing a ribbon having a lithographic substrate surface through one or more rollers with one end unwinding from a roll of unused ribbon and the other end winding up to a roll of used ribbon. The erasing means is not needed in such a system. The coating means, exposure means, and inking means are mounted proximate the passage of the ribbon and sequentially arranged along the moving direction of the ribbon.
For the above variable data lithographic printing device of this invention, the printing cylinder and the coating means can be replaced with a pre-sensitized lithographic ribbon supply means for passing a pre-sensitized lithographic ribbon through one or more rollers with one end unwinding from a roll of unused ribbon and the other end winding up to a roll of used ribbon, wherein the pre-sensitized ribbon comprises on a substrate an ink and/or fountain solution developable photosensitive layer. The erasing means is not needed. The exposure means and inking means are mounted proximate the passage of the ribbon and sequentially arranged along the moving direction of the ribbon.
For all the above devices and processes of this invention, a developing means can be added between the exposure means and inking means so that a conventional photosensitive layer that is not developable with ink and/or fountain solution can be used.
The printing device of this invention can be a typical printer wherein the inked imaging is transferred to a sheet-like receiving medium that passes through the printing device; a transfer means can be equipped after the inking means to feed the receiving medium through the printing device while pressing the receiving medium against the inked cylinder or ribbon surface. Alternatively, the printing device of this invention can be a printing wheel wherein the printing cylinder or printing device moves against the receiving surface of a stationary object during printing operation.
The current invention can be used to design various variable data printers such as desktop printer, portable printer, photoprinter, photocopier, facsimile printer, cashier receipt printer, and variable data printing wheels. The variable data printing wheels are suitable for printing variable imaging on various fixed or hard-to-feed objects such as floor, wall, road, box, a page in a book, truck, clothes, cardboard, skin, and billboard.